1. Field of the Invention
The present invention relates to compositions and processes for coating metals and, more particularly, to aqueous compositions of metals for coating metal surfaces, and processes for making these aqueous compositions.
2. Technical Background
Many methods have been developed to form new conversion surfaces on commodity metals such as ferrous metals, steel, stainless steel, aluminum, zinc and titanium. These methods include electroplating, phosphating (conversion surfaces), chemical vapor deposition, ion sputtering, and other techniques. An early electroplating method for silver was developed in England in 1870. Later, methods of plating noble metals, i.e. copper and gold were developed. These metals had to be complexed with cyanide to make an adherent deposit on the substrate material. The use of cyanide is still the preferred method of forming an adherent first deposit of noble metals on substrates. Cyanide, an extremely toxic material, is an environmental hazard and a danger to public health. Numerous safety procedures have to be in place to use cyanide, and even then users may be subjected to fumes that are dangerously toxic. As electroplating technology has unfolded over the years, techniques to electroplate other elements such as zinc, cadmium, nickel, and chromium were developed and became widely used in the commercial world for engineering and decorative purposes.
Electroplated deposits on a substrate surface do not go into the metal interstices of the surface. As a result the deposits are not tenacious enough to maintain their integrity when the substrate is “cold worked” to yield point. Zinc electrodeposits are destroyed by cold working at 61,000 PSI, cadmium at 69,000 PSI, while the steel substrate will have a yield point of 80,000 PSI or stronger. This has always been a significant problem in the electroplating industry. The electroplater has to deal with many different parameters to create efficient deposition procedures to accomplish desired end results. Electroplating requires procedures for pretreatment, pre-cleaning, and rinsing controlled plating baths, and special anodes. Electroplating generally follows the rules of the Electromotive Series that a more noble metal can be plated on a less noble metal, but not the reverse direction. This limits the ability to plate all the metals in the periodic table onto other metal substrates in the periodic table.
Another method of surface modification is phosphating, wherein a phosphate conversion surface is formed on steels and aluminum. Phosphate conversion surfaces are widely used for corrosion inhibition and as a base for paints. Phosphating is one of the most widely used techniques in the commercial world with major uses in the auto industry as an undercoat to inhibit corrosion and as an anchor to retain paint.
Conversion coating phosphating methods require large plating baths and are energy intensive and time consuming. Phosphating requires at least ten minutes or longer to get a commercially acceptable, adherent conversion surface. The industry has developed many accelerants over the years to speed up the conversion process.
In the latter part of the 20th century, new and exotic techniques were developed to obtain better surfaces on metals. These methods modified the metals with a coating on a substrate by vapor deposition techniques such as vacuum evaporation, sputtering, magnetron sputtering, or ion plating. These techniques can be used to harden metal surfaces such as metal working tools including tungsten carbide inserts, drills, hobbs, etc. Chemical vapor deposition is applied in a vacuum chamber and the metal is ionized in a nitrogen atmosphere and deposited on and diffuses into the substrates. Some examples of the results of these techniques are titanium nitride and boron nitrides. The deposition is generally by line of sight and the process is limited to the shape, size and configuration of the substrate metals. This process is expensive, requiring special equipment and high energy usage. The deposits are formed under exacting conditions of temperature, gas composition, etc. These techniques result in deposits that have dense, smooth, defect free surfaces useful for many commercial products.
Many metals form a passive oxide surface that are beneficial in protecting the metal from corrosion. Such metals are aluminum and stainless steels and titaniums. The oxide film that forms on stainless steel is a mono-molecular layer that renders the surface passive. The oxide layer that forms on carbon steel is deleterious to the metal and is called rust.
U.S. Pat. No. 6,755,917, issued to Hardin, et al. describes a solution for providing conversion coating on the surface of a metallic material. The solution includes a peroxidic species and is limited to at least one metal from Group IB, IIB, IVA, VA, VIA AND VIII of the periodic table. Specifically, Hardin also provides a liquid acidic aqueous concentrate for the replenishing of a conversion coating solution according to the invention, wherein the concentrate contains rare earth ions (as herein defined) and monovalent anions in a molar ratio of total rare earth ions:monovalent anions of from 1:200 to 1:6 and/or rare earth ions and divalent anions in a molar ratio of total rare earth ions:divalent anions of from 1:100 to 1:3 and/or the concentrate contains at least one metal selected from Groups IB, IIB, IVA, VA, VIA and VII, preferably from the group of Cu, Ag, Au, Cd, Hg, Ni, Pd, Pt, Co, Rh, Ir, Ru, Os, Sn, Pb, Sb, Bi, Se and Te and anions such that the molar ratio of the sum of the elements in this group:anions is in the range from 1:50 to 1:10,000. Further, the Hardin methods are limited to an acidic aqueous solution.
It is known that thin mono-molecular oxide films present on stainless steel can provide an excellent passivation surface to metals. It has been theorized that corrosion may one day be conquered by a thin molecular layer on metal surfaces. It has been further theorized that significant reductions in friction could be obtained with thin, tenacious metallic films.
In the October 1996 issue of Scientific American, Jacqueline Krim, PhD, published a paper titled “Friction at the Atomic Scale”. Her findings led to the conclusion that “at the atomic level with metal to metal contact there is no friction.” This surprising finding called into question many of the beliefs that friction was a condition that could only be alleviated by the use of a lubricant to reduce the heat generated by metals sliding over one another. Another surprising conclusion was that, at the atomic level, “friction arises from atomic lattice vibrations when atoms close to the surface are set into motion by the sliding action of atoms in the opposing surface. These vibrations are really sound waves. In this way, some of the mechanical energy needed to slide one surface over the other, is converted to sound energy, which is eventually transformed into heat.” Heat causes friction. To maintain the sliding, more mechanical energy must be added. Krim further posits “Solids vibrate only at certain distinct frequencies, so the amount of mechanical energy depends on the frequencies actually excited. If the atoms in the opposing surface resonates with the frequency of the other surface, then friction arises. But if the opposing surface is not resonant with any of the other surface's own frequencies, then sound waves are not generated. This feature opens the exciting possibility that sufficiently small solids, which have relatively few resonant frequencies, might exhibit nearly frictionless sliding.”
Another surprising result of her work was that dry films were slipperier than liquid films. This was counterintuitive to all current thought on friction. Further tests by other scientists validated that metal to metal contact at the atomic level eliminated friction, and that liquid lubricants caused friction with the “stick/slip” action. The liquid would stick in the gaps in the metal and then slip out. This caused vibrations in the lattices and generated sound waves which converted to heat, causing friction.
Estimates are that friction reduction could save up to 1.6% of Gross National Product or over two hundred billion dollars annually. Hence, a process that virtually eliminates friction on commodity metals would be new and useful but has never been available. It is clear that such a process would have great value and aid in the nation's quest for energy independence and greatly reduce infrastructure replacement costs for corroding metal structures, underground pipelines, storage tanks, bridges and overpasses.
Phosphate conversion surfaces are used in commercial plants to reduce decibel levels. High decibel levels are an ongoing workplace hazard and are detrimental to human health causing early hearing loss. Governmental regulatory agencies such OSHA and the EPA are constantly urging industry to develop lower decibel levels in manufacturing operations. Therefore any conversion surface that reduces decibel levels would be advantageous for human health and improving the work place environment.
U.S. Pat. No. 7,087,104 issued to Choi et al., describes a system and method for storing a solution containing a subset of a group consisting of a metal ion, a complexing agent, an ammonium salt, and a strong base. Near the time of use, the solution is used to form an electroless deposition solution containing the entire group. In one embodiment of the invention, the metal ion includes a cobalt ion, the complexing agent includes citric acid, the ammonium salt includes ammonium chloride, and the strong base includes tetramethylammonium hydroxide. The base solution is prepared and then set aside for 2 days to allow for stabilization prior to use. Another solution has to be prepared and then mixed with the first solution just prior to use in a plating bath. This requires complex logistics and skilled operators to make the final preparation at the plant bath site.
In U.S. Pat. No. 5,310,419 issued to McCoy et al. methods are disclosed for preparing electrolyte solutions for electroplating of metals and other uses. It was discovered that with the use of an external electromotive source that all metals in the Periodic table could be electrodeposited on conductive substrates. McCoy et al teach that the process of making their solutions requires adding acid and base together rapidly, producing a violent exothermic reaction to avoid ammonia loss. McCoy et al's electrolyte solutions prepared in this manner do not provide for deposition of a non-alkaline metal on a surface without the use of applied external electromotive force, and do not provide for the deposition of phosphorus or sulfur and nitrogen on a surface simultaneously with the deposition of a non-alkaline metal.
U.S. Pat. No. 5,340,788 issued to Defalco, et al., discloses a method for preparing an oil additive that is applied to parts of internal combustion engines using the lubricating oil as the carrier fluid. The solution is mixed with a polyethylene glycol for introduction into the lubricating oil.